Extreme winter weather events in North America have become more frequent and increasingly destructive. This phenomenon was linked to a jet stream pattern that generates abnormally warm conditions in the west and cold conditions in the east, referred to as the North American Winter Dipole. Studies have shown that the Dipole may have amplified and this amplification could be linked to global warming. By analyzing the atmospheric and oceanic data worldwide, the wintertime circulation in the Northern Hemisphere shows signs of a persistent change after the 1980s. In the first part of this study, we examine how the ocean has changed in correspondence to the Dipole and the evolution of the pattern change. In the second part of this study, we use multiple global reanalysis datasets to construct the Dipole index. The result validates the reported Dipole variation during the modern period. We also use the Dipole variance to investigate the Dipole’s behavior in the paleoclimate and future warming conditions. Overall, we sought to better understand how the Dipole pattern evolves and how it may link to the different forcing, as a way to anticipate future change in North America’s winter.

A large-eddy simulation methodology (LES) has been developed for predicting the turbulent physics of an incompressible flow in simple and complex geometries. The Cartesian form of the governing equations was first verified, and then later used to investigate a three-dimensional shear-driven cavity flow. The investigation involved Reynolds numbers of 2000, 3200, 5000 and 10000 and focused on the unsteadiness and turbulent characteristics of the flow. At the low Reynolds numbers (Re ~ 5000) where the cavity flow is fully laminar, direct numerical simulations (DNS) were conducted whereas the LES methodology was adopted to predict the cavity flow at the higher Reynolds number (Re = 10000). Determining the parameters in the damped subgrid scale (SGS) turbulence model for this complex flow was guided by the DNS results at Re = 5000. The SGS model was also verified against DNS results at Re = 7500 where the cavity flow was known through laboratory experimentation to be locally transitional. The LES results using the damped SGS model verified the published experimental evidence as well as uncovered new flow features within the cavity. LES computations were also carried-out of the three-dimensional shear driven cavity flow at a high Reynolds number where the SGS turbulent field was represented by a dynamic model. Lilly's least-squares expression was tested for determining Smagorinsky's coefficient in the model without ad hoc measures such as ensemble-averaging or filtering. However, zero cutoff of negative total viscosity (kinematic plus turbulent eddy viscosity) was necessary to maintain stable solutions. A discretized filter function was derived for the test filter. Both qualitative and quantitative comparisons to experimental data show that the dynamic model performed quite well. The dynamic model gave better comparisons to the experimental evidence than the damped model did. Vortex formation in the wake of a circular cylinder and their subsequent downstream transport was also numerically investigated by LES. Here however, the curvilinear form of the governing equations was necessary to perform the computations. A new generalized dynamic model was derived to represent the SGS stress field in the curvilinear space. This new model introduced the contravariant velocity components as part of the field variables. New downstream boundary conditions were also formulated to permit the shed vortices to exit with minimum disturbance. The focus of the investigation was at Re = 5600 with some verification of the computations at Re = 200 and Re = 3000. At all of these Reynolds numbers. the upstream boundary layer was laminar but the wake was fully turbulent at Re = 3000 and Re = 5600. The LES results of the many interesting characteristics of the wake showed good comparisons to the experimental data. / Ph. D.

The influence of mesoscale ocean eddies on near-surface ocean temperature, surface stress and phytoplankton communities is investigated by collocating numerous satellite measurements along with vertical profiles of oceanic temperature and salinity to the interiors of eddies identified and tracked in altimetric sea surface height maps. The surface currents associated with mesoscale ocean eddies impart a curl of the surface stress from the relative motion between surface air and water. This stress curl has a polarity opposite that of the vorticity of the eddy, thus attenuating the eddies by generating Ekman upwelling in the cores of anticyclones and downwelling in the cores of cyclones. Ekman pumping also arises from eddy-induced spatial variability of the sea surface temperature (SST) field that generates a wind stress curl in regions of crosswind SST gradients through a response of surface winds to SST-induced surface heating variations. SST-induced Ekman pumping is shown to be secondary to surface current-induced pumping in most regions of the World Ocean. Eddy-induced Ekman pumping resulting from the combination of surface current effects and air-sea interaction represents an order 1 perturbation of the background, basin-scale Ekman pumping velocities from the large-scale wind fields. In western boundary currents and equatorward-flowing eastern boundary currents, cyclonic eddies preferentially entrain water from the coastal side of the boundary current, which primes the interiors of cyclones to have phytoplankton concentrations that are elevated relative to the background. In contrast, anticyclones formed in these regions contain locally depressed phytoplankton concentrations from the offshore waters. While eddy pumping from vertical displacements of isopycnals during eddy formation can affect the biology in the interiors of cyclones during the transient stage of their development, this ecosystem response cannot be sustained because of the persistent eddy-induced Ekman downwelling throughout the rest of the eddy lifetimes. Likewise, the persistent eddy-induced Ekman upwelling in anticyclones is of little benefit because of their low phytoplankton content at the time of formation. A definitive response to eddy pumping is therefore difficult to detect from satellite observations alone. Eddies formed in regions where anticyclones preferentially entrain water with elevated phytoplankton concentrations, such as the South Indian Ocean, or in some mid-ocean gyre regions where small-amplitude eddies form (e.g., the oligotrophic South Pacific), an ecosystem response to eddy-induced Ekman pumping is observed. Conversely, cyclones in these regions entrain water that is low in chlorophyll, resulting in negative chlorophyll anomalies that are sustained by Ekman downwelling throughout the eddy lifetimes. The phytoplankton response to eddy-induced Ekman upwelling in anticyclones is seasonal, occurring only during the winter. It is proposed that the mechanism for the lack of ecosystem response to eddy-induced Ekman upwelling during the summer is the decoupling of the mixed layer from the nutricline. The observations presented in this dissertation provide a baseline from which coupled ocean circulation and biogeochemical models can be assessed. If coupled models are able to reproduce correctly the observed influence of mesoscale eddies on photoautotrophic communities, further insight into the mechanisms for this variability could be gained from the model output using the methodologies developed in this dissertation together with investigation of subsurface variability in the models below the depth to which chlorophyll can be inferred from the satellite observations. / Graduation date: 2013

Thesis (M.S.)--University of Hawaii at Manoa, 2006. / Includes bibliographical references (leaves 72-79). / x, 79 leaves, bound ill. (some col.) 29 cm

Approved for public release; distribution is unlimited / During the month of July 1987 an acoustical experiment was conducted by the United States Naval Research Laboratory (NRL) in the East Greenland Sea Marginal Ice Zone (MIZ) . Ambient noise "hot spots" or concentrated areas of relatively high noise levels were found along the ice edge using a towed array. Ambient noise levels were obtained on 27 and 28 July using AN/SSQ-57A and AN/SSQ-57XN5 calibrated sonobuoys . The temperature structure of the area was determined using XBT (ship) and AXBT (P3C aircraft) buoys placed inside and outside the ice edge. The ice edge was determined from coincident satellite photos, 90 GHz microwave imagery and P3 radar ice edge maps. Weather data (sea state and wind speed and direction) were recorded on the ship. The data seem to indicate a correlation between the high ambient noise levels of the hot spots and the presence of a large topographically controlled mesoscale eddy located at the southeastern extent of the MIZ. / http://archive.org/details/spatialvariabili00bigg / Lieutenant, United States Navy

Thesis (MTech (Oceanography))--Cape Peninsula University of Technology, 2016. / Similarities in marine fauna found off the coasts of southern Madagascar and KwaZulu-Natal (KZN, South Africa) led to the development of the “Suitcase Project”, with the aim of establishing whether eddies that form off southern Madagascar may package and transport biological material, as if in a suitcase, across the Mozambique Channel. In pursuit of this question, sampling was conducted on the southern Madagascan shelf and along a transect across a cyclonic eddy which originated off the southern tip of Madagascar, between the 15th and 23rd of July 2013. Bongo nets (300 and 500 μm-mesh) and a neuston net (900 μm-mesh) were used to collect zooplankton within the upper 200 m and at the surface, respectively. Samples were sorted for meroplankton (larval stages of fish and benthic invertebrates) under a stereo microscope, particularly seeking species known to be common to both the east coasts of Madagascar and South Africa and, thus potential indicators of connectivity between these regions. Larvae of crabs, rock lobster, and fish were used for DNA barcoding. Zooplankton biovolume and abundance were compared between the eddy core, eddy periphery and outer regions of the eddy, as well as stations from the Madagascan shelf. Mean neuston biovolume on the Madagascan (0.08 mL m-3) was not significantly higher than that in the eddy (0.06 mL m-3). Mean bongo biovolume in the upper 200 m was much higher on the Madagascan shelf (0.62 mL m-3) than in the eddy (0.16 mL m-3) although only 2 stations were sampled on the shelf. Highest biovolume in the eddy was recorded in the west eddy zone (0.25 mL m-3) and west outer zone (0.23 mL m-3), which was not statistically significantly higher than the eddy core (0.12 mL m-3) and east eddy zone (0.17 mL m-3). Meroplankton was comprised of coastal origin taxa and was most abundant on the shelf and in the eddy perimeters. Larval goat-fish, Parupeneus fraserorum was identified, a newly described mullid, and has been recorded on both the coasts of Madagascar and KZN, SA. Larvae of coastal invertebrate species identified, include the squat lobster Allogalathea elegans and camel shrimp Rhynchocinetes durbanensis. Other larval fish identified, but not found in high abundance include the families of reef associated fishes, for example: Apogonidae, Labridae, Pomacentridae, Priacanthidae, Serranidae and Sparidae. Higher zooplankton biovolumes, larval abundances and reef-associated larval assemblages found on the Madagascan shelf and in the periphery of the cyclonic eddy compared to the core in this study provide support for the suitcase hypothesis that planktonic organisms are entrained within eddies as they propagate south-westwards of the Madagascan shelf. However, further studies are required to determine whether planktonic larvae are able to cross the Mozambique Channel and reach the KZN coast in time to settle.

Thesis (Ph.D)--Aerospace Engineering, Georgia Institute of Technology, 2009. / Committee Chair: Menon, Suresh; Committee Member: Ruffin, Stephen; Committee Member: Sankar, Lakshmi; Committee Member: Stoesser, Thorsten; Committee Member: Yeung, Pui-Kuen. Part of the SMARTech Electronic Thesis and Dissertation Collection.

In view of the worsening air quality in the world, more concerns are focused on the environment. This thesis uses the technique of CFD and develops the computer model to investigate the wind and pollutant transport, as well as the chemistry of reactive pollutants in idealized two-dimensional (2D) street canyons. Three scientific questions are raised in this thesis. The first task is to find out the po- sition with the most favorable pollutant removal along the ground level over 2D idealized street canyon of different building-height-to-street-width (aspect) ratios (ARs). The di- mensionless parameter, C, represents the pollutant removal performance. In the isolated roughness regime, the two local maximum C locate at the reattachment point and the windward corner. In the wake interference regime, C is peaked on the windward side. The number of vertically aligned recirculations depends on the street depth in the skimming flow regime. The sizes of the secondary recirculation upstream and downstream deter- mine how the maximum C shifts from the street centre. After identifying the position of peaked pollutant removal rate at the ground level, the emission source should be placed with the highest constant C in order to remove the pollutants upward more quickly to safeguard the street-level air quality. After understanding the best pollutant removal in the street canyon of different ARs, the second task is to find out what AR is the most favorable for the ventilation and pollutant removal across the roof level. The three parameters, namely friction factor, air exchange rate (ACH) and pollutant exchange rate (PCH), are introduced to quantify the pressure difference to sustain the mean flow, the ventilation and pollutant removal, respectively. The turbulence contributes more than 70% to the total ACH and PCH in all the three flow regimes. By increasing the atmospheric turbulence in building geometry as well as the surface roughness, the ventilation and pollutant removal performance can be improved. The linear relation between the friction factor and ACH demonstrates the larger resistance that in turn promotes the air exchange over the roof level. The physical dispersion is studied; however atmospheric pollutants are seldom in- ert but chemically reactive instead. The last task is to include the three common air pollutants, NO, NO2 and O3, in the simple NOx ?O3 mechanism in terms of the photo- stationary state and reaction rates. The Damkohler numbers of NO and O3, DaNO and DaO3, are parameterized by the concentrations of the sources NO and O3. The normalized mean and fluctuation NO, NO2 and O3 are separately considered. The integrated pho- tostationary state (PSS) in the first canyon increases with DaO3 under the same DaNO. The integrated PSS of the second to the twelveth street canyons are compared with each case, the monotonic increase in the PSS from the second to twelveth canyon is perceived in DaNO/DaO3 1, 0.03, 0.02, 0.001 and 0.000333. Further decreases the DaNO/DaO3 to 0.000143, 0.000125, 0.000118, 0.000111 and 0.0001, the PSS is found to be non-linear and the trough appears in the fourth and fifth canyons. / published_or_final_version / Mechanical Engineering / Master / Master of Philosophy

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